I agree with Joels fish. I'm very sure my curviceps wouldn't handle a confrontation with a Firemouth.
Just as a side note Laetacara curviceps are cuaght around Santarem where the Rio Tapajos joins the Rio Amazonas.
Depending on your tank size, look at Geophagus tapajos sp. 'orange head', Apistogramma agassizii, and there is a species of checkerboard cichlid found in the Rio Tapajos as well. The geos grow to about 6 inches, and the other two cichlids mentioned are dwarf SA cichlids, reaching about 3 inches maximum.
Catfish found in the same catchment area include Corydoras ornatus and otocinclus, L260 and L262. As for tetras, Lemon tetras, Golden pencilfish and Marbled hatchetfish have all been cuaght around Santarem where the Rio Tapajos joins the Rio Amazonas.